Stefan,
Congratulations on your ~20dB SNR at 65 km, 2970 Hz, that is quite a landmark
supported by hard work.
You mentioned that the phase changes at 65 km do not seem to be from the
transmitter, and that the phase changes are slow (I could not determine how
slow from your earlier plot).
Does slow phase change (not from transmitter) lead you to suspect that the
phase changes (and some signal strength variation) may be from modal
interference (multiple rays interfering)? This question derives from modal
interference being more prevalent and greater in magnitude at lower VLF and ULF
frequencies, and distances less than 1,000 km. I didn't ask this before,
because it would be unusual for modal interference to be a substantial issue at
two widely separated locations (i.e at 65 km and at Todmorden). I didn't see
mention of this possibility in Markus' comments so I'm wondering if this
possibility is ruled out by other observations?
Your results today are great news, nice work!
73,
Jim AA5BW
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of DK7FC
Sent: Monday, December 12, 2016 9:06 AM
To: [email protected]
Subject: Re: ULF: Finally 100 mA on 2.97 kHz
Hi Paul,
FYI, it still looks like the changing phase on the spectrograms of the tree are
not caused by instabilities on the transmitter site.
Since yesterday (11.DEC) 0:22:40 UTC i'm running an unmodulated carrier right
on 2970.000 Hz. It has stopped a minute ago, 12.DEC, 14 UTC, i.e.
nearly 38 hours.
The local SNR plot shows that the interference effect can reduce the SNR by 10
dB in daylight whereas it is not present at night. But maybe this is not
relevant for you when trying to find a trace of my signal in the UK.
The signal seems to be so strong in 65 km that it may be possible to produce a
coloured spectrogram showing some diurnal phase variations...
73, Stefan
Am 08.12.2016 00:37, schrieb DK7FC:
> Hi Paul,
>
> Am 07.12.2016 14:50, schrieb Paul Nicholson:
>>
>> About 1uW should give some hint in a hour and very significant peak
>> on an 8 hour spectrum.
> I run a constant carrier from 13:30...7:00 UTC. On 7 UTC i will start
> an EbNaut transmission for my local test: 5 chars 8K19A 80s. This
> takes half a day about...
> I also added a few plots and spectrograms to follow the transmission
> from the tree
> http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html
> Also you can check the antenna current plot to get some more
> information: http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/TX.png
>
> BTW i put 5x 7 Ah accus there and am recording at 24 kS/s stereo to a
> 32 GB USB stick. The recording hast started about 15 UTC and i will
> drive there (a trip of 2x 110 km!) again sunday morning to bring it
> back. Poor accus, have to do that job below 0 C.
> So i have more than 3 day time to run various transmission tests..
>
> I'm plotting the signal level and noise level, visible on the grabber.
> At night, the signal becomes about 10 dB stronger while the noise
> increases maybe 3 dB. The antenna current is super stable however.
> What could the reason be? Propagation? I wouldn't assume that.
> I do not see this effect on 6470 Hz.
>
> Update from 23:20 UTC: I found that the time server program has
> crashed! :-( And it is an old PC so there are glitches from time to
> time. Probably this is another reason why you don't see the faintest
> signal :-( My grabber plots look quite good anyway, so maybe the
> problem hasn't been so dramatic.
> Now i'm watching the phase! And since 23:23 UTC it should be stable.
> This may also explain the lower SNR in daylight, maybe it just has to
> do with the number of phase jumps in one FFT :-( A few things don't
> run as unproblematic as i would like but at least a signal is on the
> air... I will sort out all problems by time...
>
>>
>> You made a long transmission with 30mA, from 2016-06-26_13:00 to
>> 2016-07-31_08:00, 34.79 days. No trace of the signal even with a
>> coherent daily stacking gain of 15.4dB. Wait 58 says
>> 0.036 fT for your ~100nW, which should have been visible in one day,
>> say 8 hours.
>>
>> So something is not adding up. Maybe ERP is much lower
>> than estimated, or the propagation near the mode 2 cut-off frequency
>> is more attenuated or suffering a variable phase due to dispersion.
> We will find that out! That's the interesting thing on this new land.
> And i can rise the power by another 8 dB. But later...
>
> 73, Stefan
>
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